ELECTROMAGNETIC WAVE ABSORBER USING RESISTIVE MATERIAL
An electromagnetic wave absorber includes a ground layer made of a metal conductor, a dielectric layer formed on the ground layer, and a unit cell pattern made of a resistive material, and formed on the dielectric layer. The unit cell pattern includes a fundamental patch having a regular square shape, in which a rectangular recess is formed on the center of each of the respective sides, the fundamental patch being located at the center of each of the unit cell pattern, and half cross dipole patches, which are respectively disposed at the four sides of the fundamental patch at a regular angle so as to be engaged with the recesses formed on the respective sides of the fundamental patch at a regular interval.
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The present invention claims priority of Korean Patent Application No. 10-2008-0044515, filed on May 14, 2008, which is incorporated herein by reference.
FIELD OF THE INVENTIONThe present invention relates to a resonant electromagnetic wave absorber using a resistive material, and more particularly to an electromagnetic wave absorber made of a resistive material, in which the whole pattern, obtained by periodically arranging unit cells, properly adjusts the phases of reflected waves and transmitted waves using an Electromagnetic BandGap (EBG) structure so as to absorb electromagnetic waves.
This work was supported by the IT R&D program of MIC/IITA[2007-F-043-01, Study on Diagnosis and Protection Technology based on EM]
BACKGROUND OF THE INVENTIONAs information technology (IT) has been rapidly developed and a desire for Internet communication has been increased, wireless communication instruments including a portable terminal become necessary articles for the present age. However, as portable instruments have been increasingly used, the influence of electromagnetic waves generated from the terminals on the human body becomes an important issue. The influence of electromagnetic waves at a frequency band used by portable terminals on the human body is not clearly known now, but it has been reported that the electromagnetic waves may cause leukemia, a brain tumor, a headache, a lowering of eyesight, and confusion of brain waves, destruction of men's reproductive function, and various diseases, when they are accumulated in the human body. Thus, many researches for blocking electromagnetic waves to prevent the bad influences of the electromagnetic waves on the human body are underway.
Generally, electromagnetic wave absorbers absorb electromagnetic waves using a material having an electromagnetic wave absorbing characteristics, and thus prevent the above influence of the electromagnetic waves. These electromagnetic wave absorbers are developed by a trial and error method, and thus have a complicated manufacturing process and cause a difficulty in adjusting an absorbing frequency band and absorbing characteristics.
Flat panel-type resonant electromagnetic wave absorbers, such as a λ/4 wave absorber and a Salisbury screen, include a resistive sheet, a dielectric spacer, a metal conductive ground surface, and thus have a simple constitution, are easily manufactured, and are easy to adjust an absorption performance. However, these resonant absorbers are disadvantageous in that the thickness of the dielectric spacer from the metal conductive ground surface is at least λ/4.
Accordingly, an electromagnetic wave absorber, which has a simple manufacturing process, is easy to adjust an absorbing frequency band and absorbing characteristics, and has an adjustable thickness, is required.
SUMMARY OF THE INVENTIONTherefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide an electromagnetic wave absorber made of a resistive material using an Electromagnetic BandGap (EBG) structure, which has a simple manufacturing process, and easily adjusts an absorbing frequency band and absorbing characteristics by adjusting parameters, and has an adjustable thickness.
In accordance with one aspect of the present invention, the above and other objects can be accomplished by the electromagnetic wave absorber having at least two unit cells, which are periodically arranged, each of said at least two unit cells including a ground layer made of a metal conductor, a dielectric layer formed on the ground layer and a unit cell pattern made of a resistive material, and formed on the dielectric layer. The fundamental patch and the half cross dipole patches have different surface resistance values.
In accordance with another aspect of the present invention, there is provided the electromagnetic wave absorber including a ground layer made of a metal conductor, a dielectric layer formed on the ground layer, and a unit cell pattern made of a resistive material, and formed on the dielectric layer. The unit cell pattern includes a fundamental patch having a regular square shape, in which a rectangular recess is formed on the center of each of the respective sides, the fundamental patch being located at the center of each of the plurality of unit cell patterns, and half cross dipole patches, which are respectively disposed at the four sides of the fundamental patch at a regular angle so as to be engaged with the recesses formed on the respective sides of the fundamental patch at a regular interval. The unit cell pattern further includes a first slot formed in the center of the fundamental patch. The unit cell patterns includes second slots respectively having a regular square shape, and formed at corners of the first slot. The unit cell patterns include third slots respectively formed in the half cross dipole patches. The third slots respectively have a shape of a half cross dipole. The resonant frequency and the bandwidth of the electromagnetic wave absorber are controlled by adjusting structural parameters to determine the electrical lengths of the fundamental patch and the half cross dipole patches, an interval between the fundamental patch and the half cross dipole patches, a height from the ground layer to the plurality of unit cell patterns, material characteristics for the dielectric layer, surface resistance values of the plurality of unit cell patterns, a size of the first slot, a length of one side of each of the second slots, and a size of the third slots. The unit cell patterns of neighboring unit cells, periodically arranged, have different surface resistance values. The structural parameters to determine the electrical lengths of the fundamental patch and the half cross dipole patches include a length of one side of the unit cell pattern, a length of one side of each of the half cross dipole patches, which contacts the corresponding the unit cell pattern, a length of another side of each of the half cross dipole patches, which is engaged with the fundamental patch and is parallel with the fundamental patch, a length of one side of the regular square-shaped fundamental patch, a thickness of the unit cell patterns, and a perpendicular height of each of the half cross dipole patches from one side of the plurality of unit cell patterns.
The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
Now, preferred embodiments of the present invention will be described in detail with reference to the annexed drawings.
The dielectric layer 110 and the unit cell pattern 105 made of the resistive material form a structure adding a loss to a frequency selective surface (FSS), and thus serve to partially reflect and partially transmit incident waves at a desired frequency and to adjust phases of the waves in the dielectric layer 110. Further, the metal conductive ground surface 115 serves to totally reflect electromagnetic waves, partially transmitted by the unit cell pattern 105 made of the resistive material. And, the reflected electromagnetic waves interfere and cancel one another by adjusting the phases of the electromagnetic waves in the dielectric layer 110, and thus the electromagnetic wave absorber of the present invention absorbs the electromagnetic waves.
A height 135h of the unit cell pattern 105 from the metal conductive ground surface 115, properties of the permittivity 140εr1, and magnetic permeability 140μr1 of the dielectric layer 110, and a thickness 130t of the unit cell pattern 105 serve as parameters of the absorption performance of the electromagnetic wave absorber, such that electromagnetic wave absorbing band and absorption performance of the electromagnetic wave absorber can be adjusted.
R(dB)=20×log(rDUT/rG)
Here, R represents reflectivity, rDUT represents a reflection coefficient of the electromagnetic wave absorber, and rG represents a reflection coefficient of the metal conductive ground surface. In the present invention, an absorbing band of −10 dB is decided to be a reference line 405. A frequency band having a reflectivity less than the reference line 405 of −10 dB is in the range of 5.1 GHz (410) to 7.2 GHz (415), and thus the frequency band in one embodiment is 5.1 GHz to 7.2 GHz.
By adjusting the size of the first slot 510, the first slot 510 serves to adjust an absorbing bandwidth and an absorbing performance of the electromagnetic wave absorber.
By adjusting the size of the second slots 815, the second slots 815 serve to adjust an absorbing bandwidth and an absorbing performance of the electromagnetic wave absorber, together with the first slot 810.
The size of the third slots 1320 is adjusted, and thus the third slots 1320 serve to adjust the absorbing bandwidth and an absorbing performance of the electromagnetic wave absorber, together with the first slot 1310 and the second slots 1315.
A dotted line 1625 is a reference line to determine an absorbing bandwidth. It is shown that this structure widens the absorbing bandwidth of the electromagnetic wave absorber and the bandwidth and the resonant frequency of the electromagnetic wave absorber are adjusted by the surface resistance of the fundamental patch.
The above pattern structure, in which a desired number of the unit cell patterns are arranged, improves the absorbing bandwidth of the electromagnetic wave absorber, and the bandwidth and the resonant frequency of the electromagnetic wave absorber care adjusted by adjusting the surface resistance values of the above structure.
As apparent from the above description, the present invention provides an electromagnetic wave absorber having at least two unit cells, which are periodically arranged, each of the at least two unit cells comprising a ground layer made of a metal conductor; a dielectric layer formed on the ground layer; and a unit cell pattern made of a resistive material, and formed on the dielectric layer. The electromagnetic wave absorber is capable of estimating a performance, has a simple manufacturing process compared with a general electromagnetic wave absorber, easily adjusts an absorbing frequency band and absorbing characteristics through adjusting parameters, and has an adjustable thickness compared with a conventional flat panel-type resonant electromagnetic wave absorber and thus is miniaturized.
While the invention has been shown and described with respect to the embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.
Claims
1. An electromagnetic wave absorber having at least two unit cells, which are periodically arranged, each of said at least two unit cells comprising:
- a ground layer made of a metal conductor;
- a dielectric layer formed on the ground layer; and
- a unit cell pattern made of a resistive material, and formed on the dielectric layer.
2. An electromagnetic wave absorber comprising:
- a ground layer made of a metal conductor;
- a dielectric layer formed on the ground layer; and
- a unit cell pattern made of a resistive material, and formed on the dielectric layer,
- wherein the unit cell pattern includes:
- a fundamental patch having a regular square shape, in which a rectangular recess is formed on the center of each of the respective sides, the fundamental patch being located at the center of each of the unit cell pattern; and
- half cross dipole patches, which are respectively disposed at the four sides of the fundamental patch at a regular angle so as to be engaged with the recesses formed on the respective sides of the fundamental patch at a regular interval.
3. The electromagnetic wave absorber of claim 2, wherein the resonant frequency and the bandwidth of the electromagnetic wave absorber are controlled by adjusting structural parameters to determine the electrical lengths of the fundamental patch and the half cross dipole patches, an interval between the fundamental patch and the half cross dipole patches, a height from the ground layer to the unit cell pattern, material characteristics for the dielectric layer, and surface resistance values of the unit cell pattern.
4. The electromagnetic wave absorber of claim 2, wherein the unit cell patterns further includes a first slot formed in the center of the fundamental patch.
5. The electromagnetic wave absorber of claim 4, wherein the resonant frequency and the bandwidth of the electromagnetic wave absorber are controlled by adjusting structural parameters to determine the electrical lengths of the fundamental patch and the half cross dipole patches, an interval between the fundamental patch and the half cross dipole patches, a height from the ground layer to the unit cell pattern, material characteristics for the dielectric layer, surface resistance values of the unit cell pattern, and a size of the first slot.
6. The electromagnetic wave absorber of claim 4, wherein the unit cell patterns includes second slots respectively having a regular square shape, and formed at corners of the first slot.
7. The electromagnetic wave absorber of claim 6, wherein the resonant frequency and the bandwidth of the electromagnetic wave absorber are controlled by adjusting structural parameters to determine the electrical lengths of the fundamental patch and the half cross dipole patches, an interval between the fundamental patch and the half cross dipole patches, a height from the ground layer to the unit cell pattern, material characteristics for the dielectric layer, surface resistance values of the unit cell pattern, a size of the first slot, and a length of one side of each of the second slots.
8. The electromagnetic wave absorber of claim 6, wherein the unit cell patterns includes third slots respectively formed in the half cross dipole patches.
9. The electromagnetic wave absorber of claim 8, wherein the third slots respectively have a shape of a half cross dipole.
10. The electromagnetic wave absorber of claim 8, wherein the resonant frequency and the bandwidth of the electromagnetic wave absorber are controlled by adjusting structural parameters to determine the electrical lengths of the fundamental patch and the half cross dipole patches, an interval between the fundamental patch and the half cross dipole patches, a height from the ground layer to the unit cell pattern, material characteristics for the dielectric layer, surface resistance values of the unit cell pattern, a size of the first slot, a length of one side of each of the second slots, and a size of the third slots.
11. The electromagnetic wave absorber of claim 2, wherein the fundamental patch and the half cross dipole patches have different surface resistance values.
12. The electromagnetic wave absorber of claim 1, wherein the unit cell patterns of neighboring unit cells, periodically arranged, have different surface resistance values.
13. The electromagnetic wave absorber of claim 2, wherein the unit cell patterns of neighboring unit cells, periodically arranged, have different surface resistance values.
14. The electromagnetic wave absorber of claim 3, wherein the structural parameters to determine the electrical lengths of the fundamental patch and the half cross dipole patches include:
- a length of one side of the unit cell pattern;
- a length of one side of each of the half cross dipole patches, which contacts the corresponding the unit cell pattern;
- a length of another side of each of the half cross dipole patches, which is engaged with the fundamental patch and is parallel with the fundamental patch;
- a length of one side of the regular square-shaped fundamental patch;
- a thickness of the unit cell patterns; and
- a perpendicular height of each of the half cross dipole patches from one side of the unit cell pattern.
15. The electromagnetic wave absorber of claim 5, wherein the structural parameters to determine the electrical lengths of the fundamental patch and the half cross dipole patches include:
- a length of one side of the unit cell pattern;
- a length of one side of each of the half cross dipole patches, which contacts the corresponding the unit cell pattern;
- a length of another side of each of the half cross dipole patches, which is engaged with the fundamental patch and is parallel with the fundamental patch;
- a length of one side of the regular square-shaped fundamental patch;
- a thickness of the unit cell patterns; and
- a perpendicular height of each of the half cross dipole patches from one side of the of unit cell pattern.
16. The electromagnetic wave absorber of claim 7, wherein the structural parameters to determine the electrical lengths of the fundamental patch and the half cross dipole patches include:
- a length of one side of the unit cell pattern;
- a length of one side of each of the half cross dipole patches, which contacts the corresponding the unit cell pattern;
- a length of another side of each of the half cross dipole patches, which is engaged with the fundamental patch and is parallel with the fundamental patch;
- a length of one side of the regular square-shaped fundamental patch;
- a thickness of the unit cell patterns; and
- a perpendicular height of each of the half cross dipole patches from one side of the unit cell pattern.
17. The electromagnetic wave absorber of claim 10, wherein the structural parameters to determine the electrical lengths of the fundamental patch and the half cross dipole patches include:
- a length of one side of the unit cell pattern;
- a length of one side of each of the half cross dipole patches, which contacts the corresponding the unit cell pattern;
- a length of another side of each of the half cross dipole patches, which is engaged with the fundamental patch and is parallel with the fundamental patch;
- a length of one side of the regular square-shaped fundamental patch;
- a thickness of the unit cell patterns; and
- a perpendicular height of each of the half cross dipole patches from one side of the unit cell pattern.
Type: Application
Filed: Sep 10, 2008
Publication Date: Nov 19, 2009
Patent Grant number: 8013777
Applicant: ELECTRONICS AND TELECOMMUNICATIONS RESEARCH INSTITUTE (Daejeon)
Inventors: Dong-Uk Sim (Daejeon), Jong Hwa Kwon (Daejeon), Sang Il Kwak (Daejeon), Hyung Do Choi (Daejeon)
Application Number: 12/207,818
International Classification: H01Q 17/00 (20060101);